Method and apparatus for cryoadhesion

ABSTRACT

A method and system for continuously delivering cryotreatment to a treatment device. In one embodiment, the system may include a first PID circuit in the fluid delivery line and a second PID circuit in the fluid return line, and the first and second PID circuits may operate simultaneously to continuously provide coolant to a cryotreatment device during the inflation phase, ablation phase, and warming (or thawing) phase while providing for temperature adjustment. Alternatively, the system may include a bypass line by which coolant may bypass the subcooler system and be delivered to the cryotreatment device at non-ablation temperatures during the inflation phase. During the ablation phase, coolant may flow through the subcooler system.

CROSS-REFERENCE TO RELATED APPLICATION

n/a

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The present invention relates to a method and system for deliveringcoolant to a cryotreatment device. Specifically, the present inventionrelates to a method and system for continuously delivering coolant to acryotreatment device during an inflation phase, an ablation phase, and awarming phase.

BACKGROUND OF THE INVENTION

Cryotreatment, a therapy that uses that removal of heat from tissue, isoften used to treat cardiac conditions such as cardiac arrhythmias. Inmost cryotreatment procedures, a pressurized refrigerant is circulatedwithin the tip of a cryotreatment catheter, where the refrigerantexpands and absorbs heat from surrounding tissue. As the tissue freezes,blood adjacent the treatment site may also freeze, creating an “iceball” that temporarily adheres the treatment element (for example, acryoballoon or thermally conductive area at the tip of the cryotreatmentdevice) to the tissue at the treatment site, a phenomenon calledcryoadhesion.

Cryoadhesion is advantageous in that it helps prevent the cryotreatmentdevice from moving away from the target treatment site of a beatingheart. However, research has shown that a freeze-thaw-freeze cycle moreeffectively ablates tissue than a single longer freeze-only cycle.Although more efficient lesion creation is desired, thefreeze-thaw-freeze cycle may also result in the thawing of the ice ballthat keeps the cryotreatment device in place. As a result, the devicemust be repositioned, which may be complicated and time-consuming.Further, some cryotreatment procedures, such pulmonary vein isolation(PVI), involve the use of fluoroscopy to visualize the position of thedevice and to make sure that, for example, the pulmonary vein iscompletely occluded. Fluoroscopy involves x-ray visualization;consequently, each time the ice ball thaws and the cryotreatment deviceis repositioned, the patient and the user are exposed to an increasedamount of radiation.

In most cryotreatment systems that include an inflatable treatmentelement such as a cryoballoon, the system includes an inflationreservoir that is used to inflate the cryoballoon. An ablation procedureusing systems such as this may require several stages. In the inflationstage, the inflation reservoir is filled with coolant at or near roomtemperature (that is, at temperatures not low enough to cause tissueablation), and this volume is then used to inflate the cryoballoon,allowing for device positioning before the cryoballoon reaches ablationtemperatures. The system may then enter one or more transition,ablation, evacuation, and refilling stages. Coolant flow may be stoppedduring the evacuation and refilling stages, and therefore the ice ballmay be allowed to thaw and cryoadhesion may be broken.

Such fixed initial volume systems may only be used for a specificdevice, as the size of the inflation reservoir is predetermined, andcannot be adapted for use with, for example, a different type or size ofdevice or newer generation of a device. If a user wants to substitute adifferent device, or even if a newer generation of a current device isdeveloped, the entire system may have to be replaced. Additionally,these systems are generally “on/off” and do not easily allow fortemperature modification during an ablation procedure.

Therefore, it is desirable to provide a method and system for moreefficient cryotreatment, while reducing the need for fluoroscopy. It isalso desirable to provide a continuous system that is usable with avariety of devices.

SUMMARY OF THE INVENTION

The present invention advantageously provides a method and system fordelivering cryotreatment to a treatment device. In one embodiment, thesystem may include a fluid supply; a fluid injection line incommunication with the fluid supply, the fluid injection line includinga first PID circuit having a first PID controller, a first pressuretransducer, and a first proportional valve; a cryotreatment devicehaving a treatment element in communication with the fluid injectionline; a fluid return line in communication with the cryotreatmentdevice, the fluid return line including a second PID circuit having asecond PID controller, a second pressure transducer, and a secondproportional valve; and a vacuum source in communication with the fluidreturn line, the system being programmable to operate in an inflationphase, a treatment phase, and a warming phase, the first PID circuit andsecond PID circuit simultaneously operating to control the temperatureof the treatment element during the inflation phase, the ablation phase,and the warming phase. The treatment element may define an expansionchamber, the expansion chamber being in communication with the fluidinjection line and the fluid return line, the treatment element havingan adjustable temperature based at least in part on the flow of fluidwithin the expansion chamber from the fluid supply reservoir. The systemmay further include a control unit in communication with the first PIDcircuit and the second PID circuit, first pressure transducer and thesecond pressure transducer each measuring pressure within the system,the control unit adjusting the first proportional valve and the secondproportional valve based at least in part on the pressure measurementsof the first proportional valve and the second proportional valve. Forexample, the temperature of the treatment element may be decreased whenthe first proportional valve is adjusted to increase the flow rate ofcoolant into the expansion chamber and when the second proportionalvalve is adjusted to at least partially open the expansion chamber tothe vacuum source. Likewise, the temperature of the treatment elementmay be increased when the first proportional valve is adjusted to reducethe flow rate of coolant into the expansion chamber and when the secondproportional valve is adjusted to at least partially close the expansionchamber to the vacuum source. The treatment element may be an inflatableelement, which, once inflated, may remain inflated throughout thetreatment phase and warming phase.

In another embodiment, the system may include a coolant supply; a fluidinjection line in communication with the fluid supply, the fluidinjection line including a subcooler; a bypass line in communicationwith the fluid injection line, the bypass line including a valve, aninlet upstream of the subcooler, and an outlet downstream of thesubcooler; a cryotreatment device having a treatment element incommunication with the fluid injection line; a fluid return line incommunication with the cryotreatment device; and a vacuum source incommunication with the fluid return line, the system being programmableto operate in an inflation phase, a treatment phase, and a warmingphase, the coolant continuously flowing through the bypass line duringthe inflation phase and through the subcooler during the ablation phase.The treatment element may define an expansion chamber, the expansionchamber being in communication with the fluid injection line and thefluid return line, the treatment element having an adjustabletemperature based at least in part on the flow of coolant within theexpansion chamber. The bypass valve may be substantially open during theinflation phase and substantially closed during the ablation phase.Further, the bypass line may be substantially open during the warmingphase.

In one embodiment, the method may include positioning a cryotreatmentdevice including a treatment element defining an expansion chamberproximate the area of target tissue, the expansion chamber being influid communication with a fluid flow path, and continuously deliveringcoolant to the expansion chamber during the inflation phase, theablation phase, and the warming phase, the first PID circuit operatingto deliver coolant to the expansion chamber at a first flow rate duringthe inflation phase, a second flow rate during the ablation phase, and athird flow rate during the warming phase. The fluid flow path mayinclude a fluid supply containing coolant, a fluid injection line incommunication with the fluid supply and the expansion chamber, the fluidinjection line including a first PID circuit having a first PIDcontroller, a first pressure transducer, and a first proportional valve;a fluid return line in communication with the cryotreatment device, thefluid return line including a second PID circuit having a second PIDcontroller, a second pressure transducer, and a second proportionalvalve; and a vacuum source in communication with the fluid return line,the system being programmable to operate in an inflation phase, anablation phase, and a warming phase, the first PID circuit and secondPID circuit simultaneously operating to control the flow rate of coolantinto and out of the expansion chamber during the inflation phase, theablation phase, and the warming phase.

In another embodiment, the method may generally include positioning acryotreatment device including a treatment element defining an expansionchamber proximate the area of target tissue, the expansion chamber beingin fluid communication with a fluid flow path, and continuouslydelivering coolant to the expansion chamber during the inflation phase,the ablation phase, and the warming phase, the bypass line valve beingsubstantially open during the inflation phase and substantially closedduring the ablation phase. The fluid flow path may include a coolantsupply; a fluid injection line in communication with the fluid supplyand the expansion chamber, the fluid injection line including asubcooler; a bypass line in communication with the fluid injection line,the bypass line including a valve, an inlet upstream of the subcooler,and an outlet downstream of the subcooler; a fluid return line incommunication with the cryotreatment device; and a vacuum source incommunication with the fluid return line, the system being programmableto operate in an inflation phase, an ablation phase, and a warmingphase, the coolant flowing through the bypass line during the inflationphase and through the subcooler during the ablation phase.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 shows a schematic view of a first embodiment of a continuous flowcryotreatment system in accordance with the present invention;

FIG. 2 shows a distal end of a cryotreatment device having an inflatabletreatment element;

FIG. 3 shows a graphical representation of system temperatures andcoolant flow as is achieved by a continuous flow cryotreatment system inaccordance with the present invention; and

FIG. 4 shows a schematic view of a second embodiment of a continuousflow cryotreatment system in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As described above, many currently known ablation systems are fixedinitial volume systems. In these systems, a predetermined volume offluid (e.g., coolant) that is specific to the device being used may bedelivered to a fixed initial volume (inflation) reservoir from a fluidsupply reservoir at room temperature or without being cooled. That is,the temperature is above cryotreatment or even cryocooling temperatures.For example, the initial volume of coolant may have a temperature thatis close to, or slightly above, room temperature. During this step, theinflation reservoir is closed from a vacuum source. Once the initialvolume is received within the inflation reservoir, a valve may be usedto close the inflation reservoir from the fluid supply reservoir,thereby isolating the inflation reservoir. This initial volume ofinflation fluid is a fixed volume and is specific to the cryotreatmentsystem and the device being used. Therefore, if a user changes devices(for example, uses a device with a different balloon size orconfiguration), the new device cannot be used with an existing system,unless the appropriate fixed initial volume would be the same betweenthe old and new device.

Once the inflation reservoir is filled, another valve may be used toopen the inflation reservoir to the device, wherein the fixed initialvolume inflates the cryoballoon to a predetermined inflation level.During the inflation phase, the cryoballoon may be closed to the vacuumpump or exhaust system so that the coolant does not exit thecryoballoon. After the inflation phase is over, the system enters into atransition phase, wherein a valve may be used to open, at leastpartially, the cryoballoon to the vacuum source. The ablation phase thenbegins that includes a continuous flow of coolant at ablationtemperatures. That is, one or more valves may be opened or adjusted toallow coolant to both enter and exit the cryoballoon. If a thawing phaseis desired, the injection of coolant from the fluid supply reservoir isstopped altogether. The system is then evacuated or flushed by using oneor more valves to open the fluid flow path of the system to the vacuumor exhaust system. After evacuation and if another ablation phase isdesired, the inflation reservoir is refilled with coolant. During therefilling phase, the fluid flow path of the system is open to thevacuum, except for the inflation reservoir.

In the fixed initial volume system, one or more valves in the injectionline leading to the cryotreatment device and one or ore valves in thereturn line leading from the cryotreatment device are operatedindependently during the inflation, transition, and thawing phases. Thatis, during the inflation phase, the cryotreatment device is closed tothe vacuum source and the fluid supply reservoir, but open to theinflation volume reservoir. During the transition phase, thecryotreatment device is at least partially opened to the vacuum sourceand fluid supply reservoir, but closed to the inflation volumereservoir. During the thawing phase, the cryotreatment device is fullyclosed to both inflation reservoir and fluid supply reservoir, but fullyopen to the vacuum source. The ablation phase is the only phase in whichthe cryotreatment device is open to both the fluid supply reservoir andthe vacuum source.

As used herein, the terms “cryotreatment” or “treatment” refer to thethermal treatment of tissue. In particular, this thermal treatmentinvolves the cooling of tissue to ablation or subablation temperatures.Although the continuous flow systems described herein may be well suitedfor cryoablation procedures in which tissue is permanently disrupted ordestroyed. However, it will be understood that the continuous flowsystems described herein may also be suited for other cryotreatmentprocedures in which tissue may be temporarily disrupted or destroyed, orprocedures in which tissue is cooled to temperatures above those atwhich tissue is temporarily disrupted or destroyed.

Referring now to FIG. 1, an exemplary cryotreatment device 10 is shownthat may be suitable for use in the continuous flow systems 12 describedherein. In a continuous flow system 12, a cryotreatment device 10 may beopen to both a fluid supply reservoir 14 and a vacuum source 16 duringevery phase of the procedure. Further, the continuous flow system 12does not require a transition phase to move between the inflation phaseand ablation phase. The cryotreatment device 10 is in communication withthe fluid flow path 18 of the continuous flow cryotreatment system 12,and may generally define a proximal end 20 that may by coupled to ahandle 22 and a distal end 24 that may include an inflatablecryotreatment element 26. The device 10 may be in communication with acontrol unit 28 that includes one or more controllers, processors,and/or software modules containing instructions or algorithms(collectively referred to as “computers 30”) to provide for theautomated operation and performance of the features, sequences,calculations, or procedures described herein. Further, the control unit28 may include one or more displays or screens 32, user input devices,and other components required for adjusting, monitoring, and controllingthe system 12.

As shown in the non-limiting example of FIG. 1, the inflatablecryotreatment element 26 may include an outer cryoballoon 26 a and aninner cryoballoon 26 b, at least a portion of each being coupled to theelongate body 34 of the device 10 and at least a portion of each beingcoupled to a shaft 36 that may be slidably and rotatably disposed withinthe elongate body 34 of the device 10. The inflatable cryotreatmentelement 26 may define an expansion chamber 38 in which the coolant mayexpand to cool the treatment element 26. Coolant may be delivered to theexpansion chamber 38 through an injection lumen 40 (which may includeone or more holes or openings and may be coupled to at least a portionof the shaft 36, as shown in FIG. 1) and expanded coolant may berecovered from the expansion chamber 38 through an exhaust lumen 42 incommunication with a vacuum 16. The elongate body 34 and/or the shaft 36may include one or more electrodes 44, such as mapping electrodes forrecording electrocardiogram or monophasic action potential (MAP) signalsor treatment electrodes in communication with an energy source 46 (suchas radiofrequency, ultrasound, microwave, or other energy). Althoughcryotreatment devices 10 having inflatable treatment elements 26 areshown and described herein, the continuous flow cryotreatment systems 12shown and described herein may also be used with cryotreatment deviceshaving a fixed diameter, such as focal cryotreatment catheters. Further,a cryotreatment device 10 may be used that has one or more inflatableelements 26 in any of a myriad of sizes, shapes, and configurations. Thesystem 12 may be configured to identify the cryotreatment device 10being used by a smartchip or other identifying electronic component, andto adjust system 12 parameters as needed for the safe operation of thedevice 10. Alternatively, a user may manually input the identity of thedevice 10 and the system 12 may adjust as appropriate.

Referring now to FIG. 2, a first embodiment of a continuous flowcryotreatment system 12 is shown. The cryotreatment system 12 shown inFIG. 2 may be an improvement on an existing system, such as theUniversal Gen V Cryoablation Console (Medtronic, Minneapolis, Minn.),which is a fixed initial volume system. The system 12 shown in FIG. 2 isa continuous flow system 12, and therefore may be used with any of avariety of cryotreatment devices. A cryotreatment device 10 with aninflatable or expandable treatment element 26, such as a cryoballoon,may be used with the systems 12 described herein (for example, as shownin FIG. 1). The system 12 of FIG. 2 may generally include a fluid supplyreservoir 14, one or more pressure regulators, one or more pressuretransducers, one or more valves for controlling the flow of fluid withinthe fluid flow path of the system 12, a subcooler system 48, an exhaustsystem that may include a vacuum pump 16 and fluid recovery reservoir50, and one or more proportional-integral-derivative (PID) circuits 52,54, each PID circuit 52, 54 including a PID controller 56, 58, aproportional valve 60, 62, a solenoid valve 64, 66, and a pressuretransducer 68, 70. Additionally, the system 12 may include one or morecontrollers, processors, and/or software modules containing instructionsor algorithms (collectively referred to as “computers 30”) to providefor the automated operation and performance of the features, sequences,calculations, or procedures described herein. For example, a computer 30may be in communication with one or more pressure transducers 68, 70 inthe one or more PID circuits 52, 54 for the regulation of pressure andtemperature based at least in part on pressure measurements communicatedto the computer by the one or more pressure transducers 68, 70. That is,a feedback loop may be established between, at least, a PID circuit 52,54 and the computer 30.

In the continuous flow system 12 shown in FIG. 2, an inflation reservoiris eliminated. Coolant (for example, N₂O) may be delivered from thefluid supply reservoir 14 through a pressure regulator 72, which maymaintain the coolant pressure at approximately 750 psig to approximately900 psig. The coolant may then pass through a stainless steel micronfilter 74 that traps and removes system contaminants and/or particleslarger than 0.5 micron. From the micron filter 74, the coolant may passthrough an injection (or first) proportional valve 60 (MKS) and a firstsolenoid valve 64 (S1) of the first PID circuit 52. The coolant may thenpass through the subcooler system 48, wherein the temperature of thecoolant is reduced to ablation or treatment temperatures, and any gasbubbles are removed from the coolant to ensure that the coolant is in aliquid or substantially liquid state. The subcooler system 48 mayinclude a heat exchanger 80 wherein heat is removed from the coolant,one or more compressors, one or more condensers, and/or other componentsfor subcooling the coolant. The coolant may then pass through the fluidflow path 18 to the coaxial connector of the device 10 and eventuallythe expandable treatment element 26 of the device 10. A pressure reliefvalve 82, which may be set at approximately 1200 psig, may be installedin the fluid delivery line 86 to prevent over-pressurization of thesystem 12. The fluid delivery line 86 may be in communication with theinjection lumen 40 disposed within the cryotreatment device 10 via acoaxial connector 86. Coolant may then pass through one or more lumensthe elongate body 34 of the device 10 and exit the injection lumen 40through the one or more holes or openings into the expansion chamber 38.

Upon exiting the injection lumen 40 into the expansion chamber 38, thepressurized coolant may rapidly expand. This expansion causes areduction in temperature within the expansion chamber 38 and may coolthe cryotreatment element 26 to a temperature at which the treatmentelement 26 may cool or ablate tissue. Expanded coolant may then passinto the exhaust lumen 42, which may be in communication with the returnline 88 via the coaxial connector 86. Further, the exhaust lumen 42 andreturn line 88 may be in communication with an exhaust system, which mayinclude a vacuum pump 16 and fluid recovery reservoir 50 or otherscavenging elements (not shown). When in the return line 88, theexpanded coolant may pass through one or more valves (for example, asolenoid valve 66 (S7) and return proportional valve 62 (PV)). Further,expanded coolant may travel through a three-way solenoid valve 104 (S4)before entering the fluid recovery reservoir 50 or similar scavengingelements. Coolant flow may be measured by a massflowmeter 106, locatedjust downstream of the vacuum pump 16.

The system 12 may also include one or more valves for redirecting fluidand/or venting fluid to the atmosphere. For example, a solenoid valve108 (S6) may be used to vent fluid from downstream of the subcoolersystem 48 (for example, to the fluid recovery reservoir 50 or otherscavenging component). Further a three-way solenoid valve 110 (S8) maybe used to vent to the atmosphere.

Continuing to refer to FIG. 2, the system 12 may include one or morepressure transducers 68, 70 that control the pressure of the injectionline and/or the return line. For example, the system 12 shown in FIG. 2includes a first pressure transducer 68 (PT1) upstream of thecryotreatment device 10 that is a component of a first PID circuit 52.The first PID controller 56 may drive first proportional valve 60 (MKS)that controls the injection pressure within the fluid delivery line 84.In general, this pressure may be considered to be a high pressure. Forexample, the pressure may be as high as between approximately 700 psiand approximately 760 psi. The first pressure transducer 68 (PT1) maycommunicate the internal pressure of the treatment element 26 (forexample, a pressure within the expansion chamber 34) to a user, forexample, by displaying a temperature value on a display 32 associatedwith the one or more computers 30. As a further example, the system 12shown in FIG. 2 also includes a second pressure transducer 70 (PT5)downstream of the cryotreatment device 10 that is a component of asecond PID circuit 54. The second PID controller 58 may drive secondproportional valve 62 (PV) that controls the injection pressure withinthe return line 88. In general, this pressure may be considered to be alow pressure. Coolant may pass through a second solenoid valve 66 (S7)during the ablation phase or through the proportional valve (PV) duringthe continuous flow inflation phase.

During a cryoablation procedure, the two PID circuits 52, 54 may actsimultaneously throughout the procedure to control both coolantinjection and coolant return, depending on the desired treatmenttemperature. For example, the first PID circuit 52 may operate todecrease temperature of the coolant (for example, during the ablationphase of the procedure) by adjusting the first proportional valve 60(MKS) to increase injection pressure and increase fluid flow. Further,the second PID circuit 54 may simultaneously operate to adjust thesecond proportional valve 62 (PV) to decrease pressure by opening thereturn line 88 (either partially or entirely) to the vacuum pressuregenerated by the vacuum pump 16, thereby increasing fluid flow.Conversely, the first PID circuit may operate to increase temperature ofthe coolant (for example, during the warming or thawing phase of theprocedure) by adjusting the first proportional valve 60 (MKS) todecrease injection pressure and decrease fluid flow. Further, the secondPID circuit 54 may simultaneously operate to adjust the secondproportional valve 62 (PV) to increase pressure by closing the returnline 88 (either partially or entirely) to the vacuum pressure generatedby the vacuum pump 16, thereby decreasing fluid flow. In a warming phasefollowing a cryoablation or cryotreatment phase, the treatment element26 may reach temperatures well above cryoablation or cryotreatmenttemperatures, but that are sufficiently low to maintain cryoadhesionbetween the treatment element 26 and tissue. This is possible becausethe temperature of the coolant may be adjusted without ceasing coolantflow, as in fixed initial volume systems.

Increasing the coolant pressure will generally decrease coolanttemperature, and vice versa. Additionally, the higher the flow rate ofcoolant through the treatment element 26, and the lower the temperatureof that coolant, the more heat that may be removed from adjacent tissue.As coolant flow through the system 12 and through the treatment element26 is increased, the temperature of the treatment element 26 is reduced,thus increasing the treatment element's capacity for cryoablation orcryotreatment of adjacent tissue. Unlike a fixed initial volume systemin which a continuous flow is established only during the ablationphase, and in which the coolant is delivered to the treatment element ata constant temperature until coolant flow is stopped, the PID circuits52, 54 in the system 12 of FIG. 2 allow for a continuous flow of coolantthrough the system 12 and through the treatment element 26 during theinflation phase, the cryoablation or cryotreatment phase, and a warmingor thawing phase. For example, the treatment element 26 may be allowedto reach thawing temperatures, and therefore break cryoadhesion, at theend of a procedure in order to remove the cryotherapeutic device 10 fromthe treatment site. Conversely, the treatment element 26 may bemaintained at temperatures above those at which cryoadhesion is brokenif a warming phase will be followed by an ablation phase.

Referring now to FIG. 3, a graphical representation of system 12temperatures (line “temp”) and coolant flow (line “flow”) as is achievedby a continuous flow cryotreatment system 12 in accordance with thepresent invention is shown. As shown in FIG. 3, fluid flow may increasefrom zero to between approximately 2500 standard cubic centimeters perminute (sccm) and approximately 3500 sccm during the inflation phase112. Consequently, temperature within the expansion chamber 34 may bebetween approximately 20° C. and approximately 40° C. Unlike a fixedinitial volume system, the continuous flow systems 12 described hereindo not require a transition phase. During the cryoablation orcryotreatment phase 114, the flow rate may increase to betweenapproximately 6000 sccm and approximately 7000 sccm. Consequently,temperature within the expansion chamber 34 may be between approximately−55° C. and approximately −80° C. During a warming or thawing phase 116,fluid flow may decrease to approximately 3200 sccm or below, dependingon whether warming or complete thawing is desired. FIG. 3 also shows aline representing the fluid flow and temperature of coolant within thesubcooler system (line “Sub T”), both of which remain relativelyconstant through all phases of the procedure.

Referring now to FIG. 4, a second embodiment of a continuous flowcryotreatment system 12 is shown. The system 12 of FIG. 4 may generallybe similar to the system 12 of FIG. 2; however, in the system 12 of FIG.4, the temperature of the treatment element 26 may be adjusted not bythe use of one or more PID circuits, but by including a fluid flow path118 that bypasses the subcooler 48. The cryotreatment system 12 shown inFIG. 4 may be an improvement on an existing system, such as theUniversal Gen IV Cryoablation Console, which is a fixed initial volumesystem that does not include a proportional valve on the return line.

As in shown in FIG. 4, a bypass fluid line 118 may be added that extendsfrom the PID circuit 120 to downstream of the subcooler system 48.Further, the bypass fluid line 118 may include a two-way solenoid valve122 (SX) that may be opened or substantially opened to allow coolant tobypass the subcooler system 48 and closed or substantially closed toallow coolant to enter the subcooler system 48. For example, thesolenoid valve 122 (SX) may be open to bypass the subcooler system 48during the inflation phase when it is undesirable to use coolant that iscooled to cryoablation or cryotreatment temperatures. Further, thesolenoid valve 122 (SX) may be closed during the ablation phase, whichallows coolant to flow through the subcooler system 48 in order to reachcryoablation or cryotreatment temperatures.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A continuous flow cryotreatment system, thecryotreatment system comprising: a fluid supply; a fluid injection linein communication with the fluid supply, the fluid injection lineincluding a first PID circuit having a first PID controller, a firstpressure transducer, and a first proportional valve; a cryotreatmentdevice having a treatment element in communication with the fluidinjection line; a fluid return line in communication with thecryotreatment device, the fluid return line including a second PIDcircuit having a second PID controller, a second pressure transducer,and a second proportional valve; and a vacuum source in communicationwith the fluid return line, the system being programmable to operate inan inflation phase, a treatment phase, and a warming phase, the firstPID circuit and second PID circuit simultaneously operating to controlthe temperature of the treatment element during the inflation phase, theablation phase, and the warming phase.
 2. The system of claim 1, whereinthe treatment element defines an expansion chamber, the expansionchamber being in communication with the fluid injection line and thefluid return line, the treatment element having an adjustabletemperature based at least in part on the flow of fluid within theexpansion chamber from the fluid supply reservoir.
 3. The system ofclaim 2, wherein the system further comprises a control unit incommunication with the first PID circuit and the second PID circuit,first pressure transducer and the second pressure transducer eachmeasuring pressure within the system, the control unit adjusting thefirst proportional valve and the second proportional valve based atleast in part on the pressure measurements of the first proportionalvalve and the second proportional valve.
 4. The system of claim 3,wherein the first pressure transducer measures pressure within theexpansion chamber of the cryotreatment device.
 5. The system of claim 3,wherein the temperature of the treatment element is decreased when thefirst proportional valve is adjusted to increase the flow rate ofcoolant into the expansion chamber and when the second proportionalvalve is adjusted to at least partially open the expansion chamber tothe vacuum source.
 6. The system of claim 5, wherein the temperature ofthe treatment element is increased when the first proportional valve isadjusted to reduce the flow rate of coolant into the expansion chamberand when the second proportional valve is adjusted to at least partiallyclose the expansion chamber to the vacuum source.
 7. The system of claim6, wherein the treatment element is an inflatable element, theinflatable element remaining inflated throughout the treatment phase andwarming phase.
 8. The system of claim 7, wherein the treatment elementis positioned proximate an area of target tissue during the treatmentphase and the warming phase.
 9. The system of claim 8, wherein thetemperature of the treatment element during the warming phase is lessthan approximately 0° C. but greater than a temperature at which thetreatment element ablates the target tissue.
 10. The system of claim 9,wherein the first PID circuit and the second PID circuit each furtherinclude a solenoid valve.
 11. A method for treating an area of targettissue, the method comprising: positioning a cryotreatment deviceincluding a treatment element defining an expansion chamber proximatethe area of target tissue, the expansion chamber being in fluidcommunication with a fluid flow path, the fluid flow path including: afluid supply containing coolant; a fluid injection line in communicationwith the fluid supply and the expansion chamber, the fluid injectionline including a first PID circuit having a first PID controller, afirst pressure transducer, and a first proportional valve; a fluidreturn line in communication with the cryotreatment device, the fluidreturn line including a second PID circuit having a second PIDcontroller, a second pressure transducer, and a second proportionalvalve; and a vacuum source in communication with the fluid return line,the system being programmable to operate in an inflation phase, anablation phase, and a warming phase, the first PID circuit and secondPID circuit simultaneously operating to control the flow rate of coolantinto and out of the expansion chamber during the inflation phase, theablation phase, and the warming phase; and continuously deliveringcoolant to the expansion chamber during the inflation phase, theablation phase, and the warming phase, the first PID circuit operatingto deliver coolant to the expansion chamber at a first flow rate duringthe inflation phase, a second flow rate during the ablation phase, and athird flow rate during the warming phase.
 12. A continuous flowcryotreatment system, the cryotreatment system comprising: a coolantsupply; a fluid injection line in communication with the fluid supply,the fluid injection line including a subcooler; a bypass line incommunication with the fluid injection line, the bypass line including avalve, an inlet upstream of the subcooler, and an outlet downstream ofthe subcooler; a cryotreatment device having a treatment element incommunication with the fluid injection line; a fluid return line incommunication with the cryotreatment device; and a vacuum source incommunication with the fluid return line, the system being programmableto operate in an inflation phase, a treatment phase, and a warmingphase, the coolant continuously flowing through the bypass line duringthe inflation phase and through the subcooler during the ablation phase.13. The system of claim 12, wherein the treatment element defines anexpansion chamber, the expansion chamber being in communication with thefluid injection line and the fluid return line, the treatment elementhaving an adjustable temperature based at least in part on the flow ofcoolant within the expansion chamber.
 14. The system of claim 13,wherein the bypass line valve is substantially open during the inflationphase and substantially closed during the ablation phase.
 15. The systemof claim 14, wherein the bypass line valve is substantially open duringthe warming phase.
 16. The system of claim 14, wherein the treatmentelement is an inflatable element, the inflatable element remaininginflated throughout the treatment phase and the warming phase.
 17. Thesystem of claim 15, wherein the treatment element is positionedproximate an area of target tissue during the treatment phase and thewarming phase.
 18. The system of claim 17, wherein the temperature ofthe treatment element during the warming phase is less thanapproximately 0° C. but greater than a temperature at which thetreatment element ablates the target tissue.
 19. A method for treatingan area of target tissue, the method comprising: positioning acryotreatment device including a treatment element defining an expansionchamber proximate the area of target tissue, the expansion chamber beingin fluid communication with a fluid flow path, the fluid flow pathincluding: a coolant supply; a fluid injection line in communicationwith the fluid supply and the expansion chamber, the fluid injectionline including a subcooler; a bypass line in communication with thefluid injection line, the bypass line including a valve, an inletupstream of the subcooler, and an outlet downstream of the subcooler; afluid return line in communication with the cryotreatment device; and avacuum source in communication with the fluid return line, the systembeing programmable to operate in an inflation phase, an ablation phase,and a warming phase, the coolant flowing through the bypass line duringthe inflation phase and through the subcooler during the ablation phase;and continuously delivering coolant to the expansion chamber during theinflation phase, the ablation phase, and the warming phase, the bypassline valve being substantially open during the inflation phase andsubstantially closed during the ablation phase.
 20. An improvement for afixed initial volume cryoablation system, the improvement comprising: aPID circuit including a PID controller, the PID circuit in communicationwith a fluid return line and operating simultaneously with a first PIDcircuit in communication with a fluid injection line to adjust fluidflow rate within the system, the PID circuit allowing the system tooperate as a continuous flow system.